The present invention relates to a front end hood fixedly secured to or detachably attached to a front end portion of an endoscope.
The front end hood is widely used to carry out various endoscopic treatments efficiently with safety since the front end hood provided on the front end portion of an endoscope can ensure a sufficient distance between the endoscope and an object to be subjected to the required treatment. Even if the object exists in a narrow space where the endoscope cannot be separated from the object, the front end hood ensures such a distance to enable the endoscopic observation.
For example, Japanese Patent Kokai Publication No. 9-66091 discloses an endoscope equipped with a front end hood or cap 92 in combination with a high-frequency snaring treatment tool 97 as shown in FIG. 23. The mucosa of a diseased part is previously pulled into the front end hood 92 by means of suction, and the root portion of the diseased part is then tightened and snared with the high-frequency snaring treatment tool 97.
To enable the endoscopic observation in a wide visual field, the front end hood 92 is made of an optically transparent material so that the object can be observed through the front end hood 92 in the peripheral portion of the visual field.
However, the light beam from the object to be observed is inevitably passed in an inclined manner through the front end hood 92 in the peripheral portion of the visual field as shown by an arrow in FIG. 23, and therefore, the observed image of the object in the peripheral portion of the visual field is distorted.